Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 161151
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
651 AM CDT Thu Mar 16 2017

.SHORT TERM...(Today and tonight)
Issued at 452 AM CDT Thu Mar 16 2017

For most folks, by far the biggest story of these next 24 hours
will be the surge of much-above normal temperatures, with the vast
majority of the CWA expected to reach at least 70 degrees, and
with much of the western half of the area standing a realistic
chance of topping 80 (should places such as Kearney reach 80 it
would mark the first time this year). Not surprisingly though
given such anomalous warmth, potentially critical fire weather
conditions/fire danger could come into play again primarily within
our far western Nebraska counties (Dawson/Gosper/Furnas), and a
Red Flag Warning has been hoisted solely for these 3 counties. For
all further talk of fire weather concerns (and in fact for most of
the CWA a general lack thereof), please refer to the separate
"Fire Weather" section below. Otherwise, confidence remains fairly
high in a precip-free 24 hours, despite what could be a non-zero
risk for some spotty sprinkles/light showers not too far north of
our CWA this evening. In other departments, a few models try
hinting at a chance for at least patchy light fog late tonight
mainly in our far southeast CWA along an advancing cold front, but
with better chances for this looking to remain at least slightly
to our southeast have left this possibility out of the official
forecast as well.

Taking a quick look at recent/current weather as of 430 AM:
Overall the night is playing out pretty much as expected as we
finally catch a break the from pesky, narrow snow bands of the
past few mornings, and in fact skies are mostly clear with only
some passing, fairly thin high cirrus. In the mid-upper levels,
we remain under northwest flow aloft on the backside of a large-
scale eastern CONUS trough, but the main upper jet core has
shifted well to our east. At the surface, a north-south oriented
lee trough and effective warm front is situated to our west over
the High Plains, with a modest pressure gradient supporting
generally 5-15 MPH south/southeast breezes. Although temps may
locally drop lower where winds slacken, most of the CWA is
expected to see lows bottom out in the 30-35 range.

Now looking ahead forecast-wise through today/tonight:

Today:
The flow aloft turns more westerly as a fairly low-amplitude mid-
upper disturbance tracks from the Northern Rockies into the
Dakotas. While we will likely see some occasional enhancement of
high to perhaps mid level cloud cover as the day wears on (skies
averaging between mostly sunny and partly cloudy with brief mostly
cloudy possible), we should remain precip-free. The big story is
obviously in the lower levels, as a surge of warm air spreads east
across the Central Plains in the form of a pronounced warm front,
with 850 millibar temps soaring to generally +15-20C. The first
part of the day will feature continued prevailing southerly
breezes with speeds generally 5-15 MPH (slightly higher especially
in our far east) as a surface low pressure center and associated
trough axis organizes over western NE. However, as the afternoon
wears on, this low/trough will approach and eventually enter our
CWA from the west causing winds to turn more southwesterly to
westerly, and in many areas actually decreasing in speed somewhat.
However, a notable exception (and player in our fire weather
concerns) will be in our far west where models such as the
RAP/GFS insist that the eastern fringes of a corridor of enhances
westerly winds with sustained speeds around 20 MPH/gusts to around
30 MPH will invade mid-late afternoon behind the trough. Temp-
wise, will admit that confidence is not overly high that
everywhere will actually reach the very warm values we are calling
for (especially if high cirrus ends up being thicker than
expected), but ended up leaning toward the warmer model solutions
given the overall supportive pattern and thus made little change
from previous forecast, aiming for a modest gradient from near-70
far east, mid- upper 70s central and widespread low 80s especially
western- third.

This evening/tonight:
Maintained a dry forecast, although a few models suggest that
spotty sprinkles/light showers could maybe flirt fairly close to
mainly the north/northeast fringes of our CWA in association with
the aforementioned disturbance tracking mainly from the Dakotas
toward the Great Lakes. At the surface, the late afternoon surface
trough will gradually evolve into more of a true/weak cold front
as the night wears on, with a period of perhaps very
light/variable winds this evening in the vicinity of the surface
low itself giving way to more of a steady light northerly breeze
of 10 to maybe 15 MPH later in the night, and especially post-
midnight. There are hints (especially per the NAM) of some light
fog possibly trying to develop along/just ahead of the leading
edge of this boundary in our southeast CWA post-midnight, but have
left this out as better light fog potential looks to focus
slightly southeast of our domain. Despite weak/steady cold air
advection in the low levels, given the light-but-steady north
breezes and what should be a fair amount of passing high clouds,
this is not a very ideal cooling setup tonight. If anything nudged
up low temps a degree or so, calling for a range from mid-30s far
north, low-40s central and mid-40s far southeast.

.LONG TERM...(Friday through Wednesday)
Issued at 452 AM CDT Thu Mar 16 2017

Westerly flow aloft is expected on Friday to start the extended
periods with a ridge of high pressure forecast to amplify across the
local area over the upcoming weekend. This ridge will be weakened
some early next week by a passing trough of low pressure near the
Canadian border...followed by another ridge mid-week. While this
will result in significant fluctuations in afternoon temperatures
each day...with the potential for some marginal fire weather concern
Friday...and elevated concerns on Sunday...expect primarily mild and
uneventful weather to persist through early next week before an
upper level low across the southwest emerges into the plains. This
should bring the best chance for widespread wetting precipitation to
the local area in quite a while.

For Friday...as mentioned previously...expect marginal fire weather
concerns to develop by the afternoon hours as a very mild airmass
will remain in place across the local area. While temperatures will
not be as warm as Thursday...they are still expected to climb into
the 60s across the majority of the local area...with afternoon
relative humidity values falling below 30 percent late in the day.
While temperatures will remain mild behind tonights cold
front...expect winds to be fairly gusty behind the front...which
combined with the marginal relative humidity values...warrants a bit
of extra attention to fire weather concerns Friday.

Thereafter...temperatures will continue to climb over the upcoming
weekend...peaking Sunday afternoon as a ridge of high pressure
transitions across the local area. While this ridge will bring
significantly warmer temperatures and lower relative humidities
across the local area...winds will not be extremely strong...which
should help to limit fire weather concerns. Evenso...near critical
fire weather conditions are possible...and outside of today...this
looks like the worst fire weather day of the period locally.

For early next week...expect mild temperatures to continue through
midweek as an upper level low intensifies across the desert
southwest...moving in to the plains next Thursday or Friday. While
global models diverge with both the timing and intensity of this
system...it does appear changes are in store for the local area
toward the middle/latter half of next week...with increasing
precipitation chances - including possibly even a thunderstorm or
two south of interstate 80...next Wednesday night or Thursday.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Friday morning)
Issued at 650 AM CDT Thu Mar 16 2017

General overview:
Confidence remains rather high in VFR ceiling/visibility and
precip-free conditions through the period, with only varying
degrees of mainly passing high level clouds. However, surface wind
trends are a little tricky especially beyond the first 6-9 hours
thanks to the passage of a surface low pressure system/trough and
eventually a cold front. Will go into a bit more detail regarding
winds...

Surface winds:
While sustained speeds through most of the period should average
near-to-below 12kt, there are some modest uncertainties regarding
speed, direction and timing of directional changes especially
beyond mid-afternoon as a surface trough moves in, then followed
by a cold front. In general though, at least these first 6-9 hours
should feature a prevailing southerly direction, then going more
southwesterly during the afternoon (especially at KEAR) before
going fairly light/variable for a time as a surface low moves
directly across and then finally becoming  established from the
north late this evening into the overnight hours behind the cold
front. Later issuances can certainly add some better detail to
these winds shifts as it gets closer.

Low level wind shear (LLWS):
Considered extending a formal mention of LLWS into the first few
hours of this new valid period but with most model data
supporting a fairly rapid decrease to below mentionable thresholds
(meaning generally below 30kt of shear magnitude) decided to let
it go. There are some signs that an additional period of LLWS
could occur this evening behind the passing cold front, but will
defer to next few forecasters to take a closer look for possible
inclusion.


&&

.FIRE WEATHER...
Issued at 452 AM CDT Thu Mar 16 2017

Despite afternoon temperatures soaring well-above normal across
the CWA, the vast majority of the local area should be "safe"
from critical fire weather conditions given one or more of the
following factors:
1) Relative humidity (RH) values should remain
safely above 20 percent within counties along/east of the Highway
281 corridor, with far eastern counties along Hwy 81 likely
remaining above 30 percent.
2) Sustained winds speeds/gusts should remain below 20 MPH/25 MPH
in most areas, with some of the overall-lightest winds tending to
focus within the majority of counties west of Highway 281 where
the forecasted RH values do in fact drop under 20 percent (in
other words, there is no overlap here between the lowest RH and
stronger winds).

HOWEVER, despite the above factors, a notable exception could
materialize across our extreme western column of counties
(Dawson-Gosper-Furnas), where especially models such as the RAP
and GFS insist that the very eastern fringes of a corridor of
stronger westerly winds focused within western Nebraska will
infiltrate these counties mainly after 3 PM behind a passing
surface trough, potentially resulting in 3+ hours of gusts 25+ MPH
in the presence of RH averaging 10-20 percent. Unfortunately, not
all models (including the NAM) are in agreement on these stronger
westerly breezes invading our CWA, so there is some uncertainty
here. That being said, especially given our very dry
vegetation/fuels in this area, will err on the side of caution and
issue a Red Flag Warning for these 3 counties from 3-8 PM. This
start time is obviously a little later than usual for this type of
Warning, but prior to mid-afternoon the wind speeds should remain
safely under criteria. While confidence in moderate-at-best in
this Warning technically verifying, confidence is fairly high
that these 3 counties should be the only ones in our CWA that
really have a chance to truly breach critical thresholds, as winds
speeds should dampen/diminish spreading farther east from there.

Closing with a quick review of our local fire weather thresholds:
"Critical" means the 3+ hour overlap of relative humidity (RH) of 20-
percent-or-lower and sustained winds/gusts of 20+MPH/25+MPH (in the
presence of sufficiently-dry vegetation/fuels). "Near-critical"
means the overlap of 25-percent-or-lower RH and sustained
winds/gusts of 15+MPH/20+MPH.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Red Flag Warning from 3 PM this afternoon to 8 PM CDT this
     evening for NEZ060-072-082.

KS...None.
&&

$$

SHORT TERM...Pfannkuch
LONG TERM...Rossi
AVIATION...Pfannkuch
FIRE WEATHER...Pfannkuch



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